according to the Instructor in the class I've been in for the last three days, when an ex2 instance dies, nothing that you ever do will give you access to the data that you stored on the ephemeral drive. This is not EBS storage, this is the instance storage.
Ignoring what they say and just looking at it from a practical point of view:
The odds of any new EC2 instance you fire up starting on the same hardware, and therefor having access to the data are virtually nonexistant.
If you can't get access to the drive again, journaling is not going to be any good at all.
Add to this the fact that they probably have the hypervisor either do some form of transparent encryption, or make it so that they return all zeros if you read a block you haven't written to yet (to prevent you from seeing someone else's data) and you now have no reason to even try to use a journal on these drives.